1. Field of the Invention
The present invention relates to an X-ray computer tomography (CT) apparatus and an image controlling method thereof, and more particularly, to an X-ray CT imaging apparatus and an image controlling method thereof that can obtain a tomography image of higher time resolution for a selected area of region of interest (ROI) than peripheral areas of the ROI by using a two-dimensional multi-slice detector to reduce X-ray exposure amount of an object.
2. Background of the Invention
In an X-ray CT imaging apparatus having a multi-slice detector, an X-ray source irradiates a fan-shaped X-ray beam over an object and X-ray amounts penetrated through an object are detected by each of elements of the detector provided at an opposite position of the X-ray source. The detected projection data is reconstructed to display tomography images. A two dimensional multi-slice detector including a plurality of channels along a traversing direction (x-axis) of the object has a z-axis corresponding to an image slice (row) direction so as to form an arc shaped configuration in a direction traversing the z-axis. An X-ray source and a multi-slice detector are provided in a gantry so as to be located at opposite positions with respect to each other, and are rotated around an object placed at a center position of the gantry. By rotating an X-ray source and a multi-slice detector around an object in different angles, a series of views are obtained. This operation is referred to as a “scan”.
A helical scan rotates an X-ray source and a multi-slice detector around an object with shifting the gantry along a z-axis of the apparatus so as to obtain projection data through the multi-slice detector to reconstruct a tomography of an object.
Once a total tomography image of diagnosis portion of an object is acquired by using an X-ray CT imaging apparatus including a two dimensional multi-slice detector, an operator or a doctor decides a particular diagnosis portion in the total tomography image (hereinafter referred to as a “region of interest (ROI)”). For example, a cardiac portion is selected as an ROI. It is a technology to successively perform a plurality of scans in order to obtain dynamic images of a cardiac as an ROI or to obtain a three dimensional (3D) image data by collecting a plurality of projection data of the same phases through a cardiac synchronized reconstruction process.
However, in the background technology, while it is required to obtain projection data of a narrow range covering an ROI only in a total tomography image of an object, it has been necessary to perform a plurality of scans to obtain wide range projection data of a whole diagnosis portion including an ROI to obtain higher time resolution images. Consequently, the background technology has serious problems and defects of needing an increase of exposure amount to an object to obtain higher time resolution images of a cardiac dynamic image.